Class 12 Biology Biodiversity and Conservation Cause of biodiversity loss

Cause of biodiversity loss

  • Habitat loss and fragmentation
  • Tropical rain forests covering more than 14 per cent of the earth’s land surface, these rain forests now cover no more than 6 per cent.
  • The Amazon rain forest called as the ‘lungs of the planet’ harboring probably millions of species is being cut and cleared for cultivating soya beans or for conversion to grasslands for raising beef cattle.
  • Breaking of large areas into small fragments cause biodiversity loss.



Fig. tropical rain forest 

  • Over exploitation
  • Many species extinctions in the last 500 years were due to overexploitation by humans. For example- Steller’s sea cow, passenger pigeon.



Fig. passenger pigeon 

  • Alien species invasions
  • When alien species are introduced these cause decline or extinction of indigenous species.

Example- the Nile perch introduced into Lake Victoria in east Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake.

  • Introduction of the African catfish Clarias gariepinus for aquaculture purposes is posing a threat to the indigenous catfishes in our rivers.


Fig. African cat fish 

  • Co-extinctions
  • When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct.


  •  When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate.
  • In plant-pollinator mutualism extinction of one invariably leads to the extinction of the other.

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